[vte] build: Build fix for netbsd

[Christian Persch <chpe src gnome org>]

commit 2f255b2045fe5571c80fc9ded70af7f144ac839b
Author: Christian Persch <chpe src gnome org>
Date:   Fri Aug 5 21:04:10 2022 +0200

    build: Build fix for netbsd
    
    Define _NETBSD_SOURCE to get all necessary defines exposed, as found
    from a patch in netbsd ports.

 meson.build | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index 58410d14..70455b02 100644
--- a/meson.build
+++ b/meson.build
@@ -221,12 +221,19 @@ libc_feature_defines = [
   ['_XOPEN_SOURCE_EXTENDED', '1'],
 ]
 
-if host_machine.system() == 'freebsd'
+system = host_machine.system()
+
+if system == 'freebsd'
   # Defining _POSIX_C_SOURCE above makes freebsd not expose some functionality
   # that's hidden behind __BSD_VISIBLE.  Not defininy any of the above however
   # makes it expose verything.
 
   libc_feature_defines = []
+
+elif system == 'netbsd'
+  libc_feature_defines += [
+    '_NETBSD_SOURCE',
+  ]
 endif
 
 foreach f: libc_feature_defines